1. Field of the Invention
The present invention relates to a cam mechanism of a lens barrel which includes a first ring member (e.g., a cam ring) and a second ring member (e.g., a lens frame) supporting a part of a lens system, wherein the first ring member is rotated to move the second ring member linearly along the optical axis of the lens system.
2. Description of the Related Art
In conventional zoom lenses (zoom lens barrels), it is often the case that a lens support ring which supports a part of a zoom lens system is linearly moved along the optical axis thereof by rotation of a cam ring which is driven to rotate. The cam ring includes a plurality of cam grooves which are formed on a peripheral surface of the cam ring to have the same reference cam diagrams, while the lens support ring that is linearly guided along the optical axis includes a corresponding plurality of cam followers which are engaged in the plurality of cam grooves of the cam ring, respectively. The plurality of cam grooves, which have the same reference cam diagrams, and the plurality of cam followers are generally arranged at equi-angular intervals of 120 degrees.
However, a substantial reduction in diameter of the cam ring of a zoom lens in order to miniaturize the cam ring causes adjacent cam grooves of the cam ring to be formed so as to intersect each other on the cam ring, which may cause each cam follower to come off the associated cam groove if the plurality of cam grooves and the plurality of cam followers are simply arranged at equi-angular intervals of 120 degrees.
In addition, there is a sufficient possibility of the relationship between the plurality of cam grooves and the plurality of cam followers being applied to a moving mechanism for moving a focusing lens group or any other optical element, not only to a power-varying lens-group of a zoom lens optical system.